Date of Award

Winter 2003

Project Type

Dissertation

Program or Major

Engineering: Chemical

Degree Name

Doctor of Philosophy

First Advisor

Dale P Barkey

Abstract

Trace organic additives are known to be essential in obtaining desired metal electrodeposits in the microelectronic industry, however, fundamental design principles for their use and a scientific understanding of their interaction during electrodeposition is lacking. In the present study we investigated electrodeposition of copper on the Cu(100) surface in air-saturated or dearated acid-sulfate plating solutions containing several combinations of chloride and additives benzotriazole (BTA) and 3-mercapto propane sulfonic acid (MPSA) under galvanostatic pulse-current conditions. The electrodeposition process was followed using in-situ atomic force microscopy (AFM). AFM images were quantitatively analyzed by pattern-recognition and scaling procedures.

In the absence of additives, copper deposits grew in a layer-by-layer mode from the earliest stage of deposition. The surface consisted of smooth terraces separated by steps. The scaling analysis result was consistent with a process dominated by surface diffusion and step growth.

In chloride containing solutions, square-pyramidal mounds were initiated and grew to cover the surface. Mound slope increased with deposition time with no indication of reaching a steady-state value. This growth mode was consistent with a surface diffusion mechanism. The scaling result was similar to the additive-free system, but indicated that surface diffusion was more dominant in the presence of chloride.

BTA inhibited the surface and produced nucleation-limited growth at hemispheroidal centers whose height to base radius aspect ratio increased linearly with deposition time. Nucleation and growth of three-dimensional nodules started randomly across the entire surface. The nodules were smaller in size than the mounds observed without BTA. The number and density of nodules were much higher than the mounds density. The deposit growth was dominated by a roughening mechanism that can be described by the random roughening term of a stochastic model.

In the presence of MPSA, growth was not confined to nucleation centers, and the (100) symmetry was visible in the main features. However, pyramidal mounds did not develop. None of the existing models described sufficiently the surface growth mechanism for this case.

Roughening of copper deposits in oxygen-free solution was faster than in oxygen-saturated solution. The results of scaling analysis and pattern-recognition analysis were in agreement with kinetic studies conducted by other researchers. The presence of dissolved oxygen in solutions did not remarkably affect the scaling behavior for each examined solution.

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